1. Field of the Invention
This invention relates to load-carrying vehicles such as mobile cranes and fork lift trucks which run on ground engaging wheels.
2. Description of Prior Art
It has hitherto been proposed to provide fork lift trucks with additional road wheels movable from an inoperative position clear of the ground or a non load bearing position to an operative position in engagement with the ground outside the front wheels of the vehicle disposed generally beneath or adjacent to the load lifting mast. Such additional wheels moved vertically between the inoperative and operative positions and thus increased the overall width of the truck. Also such wheels were moved up and down by power operated means, such as hydraulic rams, actuated automatically in response to the raised load carried by or being lifted by the mast of the truck, or they may be operated at will by the driver over-riding the automatic means. In one construction the additional wheels were raised and lowered by hydraulic rams in circuit with the ram which raised and lowered the fork carriage riding up and down the mast. In such a system the forces on the front axles of the truck road wheels vary for a given load on the forks.
In many applications fork lift trucks are used in confined spaces such as between stacks of timber or in the holds of ships or through restricted warehouse doorways or enter and travel vertically in lifts from deck to deck. In such cases the conventional trucks are constructed to be passed through the openings, restricted doors and lifts with the minimum of clearance each side. Also where loads to be lifted by the forks are often in somewhat inaccessible places the forks have to engage under the loads on a long load centre so that in the known constructions the additional wheels could prevent the load being reached and lifted due to the extra width resulting from the additional road wheels which is disadvantageous. Moreover the additional wheel interfers with access for servicing and wheel changing of the front road wheels of the truck.
The main object of the present invention is to provide load lifting vehicles such as mobile cranes or fork lift trucks with such additional road wheels in which the aforesaid disadvantages are reduced compared with known constructions.